An intermetallic material is a material that comprises a plurality of metallic elements. Intermetallic materials, in which one of the metallic elements is a refractory metal, are used in the aviation and aerospace industries. Refractory-metal intermetallics are sometimes used in aircraft parts because of their light weight and durability compared to other metals. In the aviation and aerospace industry, refractory-metal intermetallics are usually formed at temperatures of at least 800 degrees Celsius. Such a high temperature of formation is unacceptable for the semiconductor industry. The intermetallics are usually part of a contact, interconnect, or via and are formed relatively late in a semiconductor process flow (after a silicide layer or doped regions, such as emitter or source/drain regions, have been formed). Heating a substrate to a temperature higher than about 700 degrees Celsius is generally undesired.
Within the semiconductor industry, intermetallic materials are being investigated to examine their ability to reduce electromigration and oxidation of metals within contacts or interconnects. An example of an intermetallic used in the semiconductor industry is titanium aluminide (TiAl.sub.3). Titanium aluminide may be formed by sputtering or evaporating a layer of aluminum, sputtering or evaporating a layer of titanium, and reacting the layers to form titanium aluminide. This method of forming titanium aluminide is actually a type of solid--solid reaction because one solid reacts with another solid.
Although the solid--solid reaction that forms titanium aluminide is typically performed at a temperature less than 700 degrees Celsius, the process suffers from several detriments. As used in this specification, intermetallic step coverage is defined as the thickness of the intermetallic layer at its thinnest point along the side of a patterned metal layer divided by the thickness of the intermetallic layer formed on the top of the patterned metal layer. The intermetallic step coverage is expressed as a percentage. Using the solid--solid reaction that forms titanium aluminide, the intermetallic step coverage is typically no more than 10 percent and may even reach 0 percent in which case, the titanium aluminide is not formed along all of the sides of the aluminum layer. Electromigration, oxidation, and hillock formation may not be sufficiently reduced in a lateral direction because of the lower intermetallic step coverage. The unreacted titanium may: 1) form undesired electrical connections because of etch complications, 2) have undesired reactions before forming or with subsequently formed layers that contact the unreacted titanium, or 3) complicated a subsequent patterning step during the formation of interconnects.